Method and system for DC compensation and AGC

ABSTRACT

A technique for performing AGC and DC compensation in a receiver. The receiver comprises an energy estimator for generating an estimate of the level of a received signal; an RF device to apply gain to the received signal; an AGC for controlling the RF device gain based on the energy estimation; a first DC compensation loop for finely adjusting the DC component of the received signal in fast or slow tracking mode (FTM or STM); and a second DC compensation loop for coarsely adjusting the DC component of the received signal. Three modes of AGC operations: In Acquisition, iterations of FTM fine DC adjustment, short energy estimation, and RF device gain adjustment are performed during signal timing detection. In Connected, long energy estimation, RF device gain adjustment, and STM fine and coarse DC adjustments are performed during superframe preamble. In Sleep, FTM fine DC adjustment, short energy estimation, and RF device gain adjustment are performed during superframe preamble.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of the filing date of ProvisionalApplication Ser. No. 61/040,663, filed on Mar. 29, 2008, and entitled“Method and System for DC Compensation and AGC,” which is incorporatedherein by reference.

FIELD

This disclosure relates generally to a system and method for automaticgain control (AGC) and direct current (DC) voltage compensation in afront-end radio frequency (RF) receiver system.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, 3GPP LTE systems, andorthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless terminals.Each terminal communicates with one or more base stations viatransmissions on the forward and reverse links. The forward link (ordownlink) refers to the communication link from the base stations to theterminals, and the reverse link (or uplink) refers to the communicationlink from the terminals to the base stations. This communication linkmay be established via a single-in-single-out (SISO) system,multiple-in-signal-out (MISO) system, or a multiple-in-multiple-out(MIMO) system.

A MIMO system employs multiple (N_(T)) transmit antennas and multiple(N_(R)) receive antennas for data transmission. A MIMO channel formed bythe N_(T) transmit and N_(R) receive antennas may be decomposed intoN_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}. Each of the N_(S) independentchannels corresponds to a dimension. The MIMO system can provideimproved performance (e.g., higher throughput and/or greaterreliability) if the additional dimensionalities created by the multipletransmit and receive antennas are utilized.

A MIMO system supports a time division duplex (TDD) and frequencydivision duplex (FDD) systems. In a TDD system, the forward and reverselink transmissions are on the same frequency region so that thereciprocity principle allows the estimation of the forward link channelfrom the reverse link channel. This enables the access point (AP) toextract transmit beam forming gain on the forward link when multipleantennas are available at the access point (AP).

In such systems, the signal at a receiver, such as the receiver of awireless access terminal (AT), may vary substantially in power level dueto a number of factors, including transmit power, mobility, multipath,fading, interference and others. At such receiver, the received signalis typically amplified by a low noise amplifier (LNA), down-converted toa lower frequency range by a mixer-local oscillator (LO) combination,and converted into digital format by an analog-to-digital converter(ADC). In order to properly or optimally convert the signal into digitalformat, the average signal power level at the input of the ADC should belarge enough that the quantization-to-noise ratio is sufficiently largeto properly quantized the received signal with minimal noise, and smallenough to prevent saturation of the ADC. Thus, in order to properly setthe signal power level at the input of the ADC, typically such receiversemploy automatic gain control (AGC) to adjust the gain of a deviceupstream from the ADC.

Another issue that arises in such receivers is the DC level produced atthe output of the downconverting mixer and other devices downstreamthereof. The DC level is mainly produced by the LO signal leakingtowards the input, and then re-mixing with the LO signal again toproduce the DC level. Generally, the DC level adversely affects theestimation of the received signal power level performed downstream. Thisestimation is performed to properly set the gain of the LNA as well as adigital gain stage further downstream.

Generally, the AGC of the LNA or mixer gain and the DC level are notindependent of each other. For example, changing the gain of the LNA ormixer often causes the DC level to change as well. Thus, there is a needfor a technique to perform AGC and DC level compensation in a combinedfashion to ensure proper signal level at the input of the ADC, as wellas a reduction or elimination of the DC level downstream of the mixer.

SUMMARY

An aspect of the disclosure relates to an apparatus and method forproviding automatic gain control (AGC) and direct current (DC)compensation in a receiver. In this regard, the receiver comprises anenergy estimator for generating an energy estimate of the signal levelof a received radio frequency (RF) signal; an RF device (e.g., a lownoise amplifier (LNA) or mixer) to apply a programmable gain to thereceived RF signal; an AGC module for controlling the gain of the RFdevice based on the energy estimation of the received RF signal, a fineDC compensation loop for adjusting the DC component of the receivedsignal in a fine manner; and a coarse DC compensation loop for adjustingthe DC component of the received signal in a coarse manner. At leastthree modes of operations are contemplated: Acquisition mode, Connectedmode, and Sleep mode.

In the Acquisition mode, the signal is being received by the receiver,but timing information of the signal has not yet been detected.Acquisition mode may be applicable just after powering up an accessterminal (AT). In this mode, an objective is to perform a reasonablyaccurate adjustment of the AGC of the received signal. This isaccomplished by performing one or more iterations of the following: (1)a fine adjustment in a fast tracking mode (FTM) of the DC component ofthe received signal; (2) a relatively brief estimation of the energy ofthe received signal; and (3) an adjustment of the programmable gain ofthe RF device based on the brief energy estimation of the receivedsignal.

In Connected mode, the receiver has detected the timing information ofthe received signal. Accordingly, an objective is to perform a moreaccurate AGC of the received signal. This is accomplished by performingone or more iterations of the following: (1) a relatively lengthyestimation of the energy of the received signal; (2) an adjustment ofthe programmable gain of the RF device based on the lengthy energyestimation of the received signal; (3) a fine adjustment in a slowtracking mode (STM) of the DC component of the received signal; and (4)one or more coarse adjustments of the DC component of the receivedsignal. If no adjustment of the programmable gain is performed in step(2), then steps (3) and (4) may be foregone, unless the fine DCcomponent of the received signal is above a predetermined threshold.

In Sleep mode, the receiver is not receiving or transmitting trafficinformation, but is receiving a quick page signal from an access point(AP). The receiver wakes up (e.g., transitions from a low power mode toa high power mode) at a predetermined time to listen to the quick pagesignal (e.g., the second symbol of the Ultra Mobile Broadband (UMB)superframe preamble (SFPA)) to determine whether the access point (AP)has a message to send to the receiver. An objective is to perform amoderately accurate AGC of the received signal fast enough after wakingup. This is accomplished by performing a predetermined number ofiterations of the following at a predetermined timing relationship withthe received signal: (1) a fine adjustment in FTM of the DC component ofthe received signal; (2) a relatively brief estimation of the energy ofthe received signal; and (3) an adjustment of the programmable gain ofthe RF device based on the brief energy estimation of the receivedsignal.

Other aspects, advantages and novel features of the present disclosurewill become apparent from the following detailed description of thedisclosure when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 illustrates an exemplary multiple access wireless communicationsystem according to an aspect of the disclosure.

FIG. 2 illustrates a block diagram of an exemplary communication systemaccording to another aspect of the disclosure.

FIG. 3 illustrates a block diagram of an exemplary receiver front-endsystem including AGC/DC compensation control according to another aspectof the disclosure.

FIG. 4 illustrates a diagram of an Ultra Mobile Broadband (UMB)superframe structure according to another aspect of the disclosure.

FIG. 5 illustrates a flow diagram of an exemplary method of calibratingthe coarse DC compensation for all AGC states according to anotheraspect of the disclosure.

FIG. 6 illustrates a flow diagram of an exemplary method of performingAGC and DC level compensation in acquisition andacquisition-to-connected-transition modes according to another aspect ofthe disclosure.

FIG. 7 illustrates a flow diagram of an exemplary method of performingAGC and DC level compensation in connected mode according to anotheraspect of the disclosure.

FIG. 8 illustrates a flow diagram of an exemplary method of performingAGC and DC level compensation in sleep mode according to another aspectof the disclosure.

FIG. 9 illustrates a block diagram of exemplary automatic gain control(AGC) module according to another aspect of the disclosure.

FIG. 10 illustrates a block diagram of exemplary direct current (DC)compensation loops according to another aspect of the disclosure.

DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as Code Division Multiple Access (CDMA)networks, Time Division Multiple Access (TDMA) networks, FrequencyDivision Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA)networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms“networks” and “systems” are often used interchangeably. A CDMA networkmay implement a radio technology such as Universal Terrestrial RadioAccess (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) andLow Chip Rate (LCR). cdma2000 covers IS-2000, IS-95 and IS-856standards. A TDMA network may implement a radio technology such asGlobal System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). Long TermEvolution (LTE) is an upcoming release of UMTS that uses E-UTRA. UTRA,E-UTRA, GSM, UMTS and LTE are described in documents from anorganization named “3rd Generation Partnership Project” (3GPP). cdma2000is described in documents from an organization named “3rd GenerationPartnership Project 2” (3GPP2). These various radio technologies andstandards are known in the art. For clarity, certain aspects of thetechniques are described below for LTE, and LTE terminology is used inmuch of the description below.

Single carrier frequency division multiple access (SC-FDMA), whichutilizes single carrier modulation and frequency domain equalization isa technique. SC-FDMA has similar performance and essentially the sameoverall complexity as those of OFDMA system. SC-FDMA signal has lowerpeak-to-average power ratio (PAPR) because of its inherent singlecarrier structure. SC-FDMA has drawn great attention, especially in theuplink communications where lower PAPR greatly benefits the mobileterminal in terms of transmit power efficiency. It is currently aworking assumption for uplink multiple access scheme in 3GPP Long TermEvolution (LTE), or Evolved UTRA.

FIG. 1 illustrates an exemplary multiple access wireless communicationsystem according to an aspect of the disclosure. An access point 100(AP) includes multiple antenna groups, one including 104 and 106,another including 108 and 110, and an additional including 112 and 114.In FIG. 1, only two antennas are shown for each antenna group, however,more or fewer antennas may be utilized for each antenna group. Accessterminal 116 (AT) is in communication with antennas 112 and 114, whereantennas 112 and 114 transmit information to access terminal 116 overforward link 120 and receive information from access terminal 116 overreverse link 118. Access terminal (AT) 122 is in communication withantennas 106 and 108, where antennas 106 and 108 transmit information toaccess terminal (AT) 122 over forward link 126 and receive informationfrom access terminal (AT) 122 over reverse link 124. In a FDD system,communication links 118, 120, 124 and 126 may use different frequencyfor communication. For example, forward link 120 may use a differentfrequency than that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access point (AP).In the embodiment, antenna groups each are designed to communicate toaccess terminals (ATs) in a sector of the areas covered by access point(AP) 100.

In communication over forward links 120 and 126, the transmittingantennas of access point (AP) 100 utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals (ATs) 116 and 122. Also, an access point (AP) usingbeamforming to transmit to access terminals (ATs) scattered randomlythrough its coverage causes less interference to access terminals (ATs)in neighboring cells than an access point (AT) transmitting through asingle antenna to all its access terminals (ATs).

An access point (AP) may be a fixed station used for communicating withthe access terminals (ATs), and may also be referred to as an accesspoint (AP), a Node B, a base station (BS), or some other terminology. Anaccess terminal (AT) may also be called a user equipment (UE), awireless communication device, a terminal, or some other terminology.

FIG. 2 illustrates a block diagram of an exemplary communication system200, such as a MIMO system, comprising a transmitter system 210 (alsoknown as the access point (AP)) and a receiver system 250 (also known asthe access terminal (AT)). At the transmitter system 210, traffic datafor a number of data streams is provided from a data source 212 to atransmit (TX) data processor 214.

In an embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 a-t receives and processes a respective symbolstream to provide one or more analog signals, and further conditions(e.g., amplifies, filters, and upconverts) the analog signals to providea modulated signal suitable for transmission over the MIMO channel.N_(T) modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna is provided to a respective receiver (RCVR) 254 a through 254 r.Each receiver 254 a-r conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 a-r based on a particularreceiver processing technique to provide N_(T) “detected” symbolstreams. The RX data processor 260 then demodulates, deinterleaves, anddecodes each detected symbol stream to recover the traffic data for thedata stream. The processing by RX data processor 260 is complementary tothat performed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use.Processor 270 formulates a reverse link message comprising a matrixindex portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224 a-t, conditioned by receivers 222 a-t,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reverse link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

FIG. 3 illustrates a block diagram of an exemplary receiver front-endsystem 300 for performing automatic gain control (AGC) and DCcompensation control according to another aspect of the disclosure. Inthe exemplary embodiment, the front-end system 300 is described hereinas part of an access terminal (AT), and, for example, may be implementedin any one or more of the receivers 254 a-r of access terminal (AT) 250,previously described. However, it shall be understood that the front-endsystem 300 may be implemented in any receiver, including any one or moreof the receivers 222 a-t of access point (AP) 210, previously described.

In particular, the front-end system 300 comprises an antenna 302, afirst switch SW1, a low noise amplifier (LNA) 304, a mixer 306, a firstsummer 308, and an analog-to-digital converter (ADC) 310 comprising ananti-aliasing filter (AAF) 312 and a sigma-delta-modulator (SDM) 314. Itshall be understood that components of the ADC 310 may be changedaccording to design preference. Additionally, the front-end system 300comprises a group delay (GD) 316, a digital filter (DF) 318, a secondsummer 320, a notch filter (NF) 322, an I/Q mismatch compensating device324, a frequency rotator (FR) 326, a digital gain module 328, a digitalsignal processing module 342, and a front-end controller 344. Further,the front-end system 300 comprises a digital DC correction loop (DDCL)330, a second switch (SW2), an analog DC correction loop (ADCL) 340, adigital-to-analog converter (DAC) 338, and an automatic gain (AGC)module 332 comprising an energy estimator (EE) 334 and a digitalvariable gain amplifier (DVGA) 336.

In operation, the antenna 302 picks up a received RF signal from awireless medium, and provides it to the LNA 304 by way of the firstswitch SW1 when it is in a closed position. The LNA 304, in turn,amplifies the received RF signal with a gain controlled by the AGCmodule 332. The amplified RF signal generated by the LNA 304 is appliedto the mixer 306, which frequency down converts the received signal to alower frequency more suitable for digital processing. The mixer 306performs the down conversion using a local oscillator (LO) signal F_(c).The mixer 306 gain is also controlled by the AGC module 332. Thedownconverted received signal is applied to an input of the first summer308, which sums the received signal with a coarse DC compensation signalgenerated by the ADCL 340 and DAC 338 in order to reduce the DCcomponent of the received signal at the output of the mixer 306. Aspreviously discussed in the Background section, the LO signal leaking tothe input of the mixer 306 and remixing with the LO signal produces a DCcomponent at the output of the mixer 306. If not corrected, the DCcomponent may propagate down the chain of modules of the front-endsystem 300.

The output of the first summer 308 is coupled to the ADC 310, whichconverts the received signal from analog to digital format. Inparticular, the AAF 312 filters the received analog signal to reduce oreliminate aliasing distortion, and the SDM 314 converts the filteredsignal into digital format. The GD 316 delays the I-component and/orQ-component of the received signal to more equalize the timingrelationship of the I/Q components. The DF 318 reduces or eliminatesjamming and/or other unwanted signals from the received signal. Theoutput of the DF 318 is applied to an input of the second summer 320,which sums the received signal with a fine DC compensation signalgenerated by the DDCL 330 in order to further reduce any DC residualremaining from the coarse DC compensation performed by the ADCL 340.

The output of the second summer 320 is applied to the NF 322, whichreduces any unwanted higher-order harmonics of the received signal. Theoutput of the NF 322 is applied to the I/Q mismatch compensating device324, which better equalizes the gains and phases associated with the I-and Q-components. The output of the I/Q mismatch compensating device 324is coupled to the FR 326, which corrects the received signal forunwanted frequency offset in the LO signal F_(c). The output of the FR326 is coupled to an input of the AGC module 332, which estimates thepower level of the received RF signal at the input of the LNA 304, andgenerates the AGC signal for the LNA 304 and the digital gain controlsignal for the digital gain module 328. The AGC signal is also used bythe DDCL 330 and ADCL 340 for adjusting the filtering of the signalsfrom the second summer 320 and the DDCL 320, respectively. The output ofthe FR 326 is coupled to an input of the digital gain module 328, whichapplies gain to the received signal based on the digital gain controlsignal generated by the AGC module 332.

The AGC signal from the AGC module 332 may adjust the gain of the LNA304 and/or mixer 306 in relatively large steps. For example, given adynamic range for the received RF signal of −110 to −20 dBm, the AGCsignal may provide the following five (5) analog gain stages for theLNA: 62 dB, 46 dB, 37 dB, 26 dB, and 10 dB. The digital gain controlsignal from the AGC module 332 provides finer gain adjustment for thereceived signal. The output of the digital gain module 342 is coupled tothe digital signal processing module 342 for further processing of thereceived signal in order to obtain the data. The digital signalprocessing module 342 may provide the controller 344 signal timinginformation or lack thereof, which the controller 344 uses to controlvarious modules of the front-end system 300. In particular, thecontroller 344 controls the AGC module 332, DDCL 330, ADCL 340, firstswitch SW1, and second switch SW2. The controller 344 may perform thecontrolling under the instructions of one or more software modulesstored in a computer readable medium.

As previously discussed, the DDCL 330 provides fine adjustment (e.g.,reduction or cancellation) of the DC component at the output of thesecond summer 320. In particular, the DDCL 330 includes an input coupledto the output of the second summer 320 in order to sense the receivedsignal including the DC component. As discussed in more detail furtherherein, the DDCL 330 generates the fine DC compensation signal byperforming a first-order filtering operation based on the gain state ofthe AGC signal. Also, as previously discussed, the ADCL 340 providescoarse adjustment (e.g., reduction or cancellation) of the DC componentat the output of the first summer 308. In particular, the ADCL 340includes an input coupled to the DDCL 330 via the switch SW2 to receivea signal therefrom related to the non-DC component of the receivedsignal at the output of the second summer 320. As discussed in moredetail further herein, the ADCL 340 generates the coarse DC compensationsignal by performing a first-order filtering operation of the DDCLsignal based on the gain state of the AGC signal.

Slow tracking mode (STM) means that the time constant of the DDCL 330 isconfigured relatively large (e.g., 102.4 μs in Connected mode) orconversely the bandwidth of the DDCL 330 is configured relatively small(e.g., 1.5 KHz). Fast tracking mode (FTM) means that the time constantof the DDCL 330 is configured relatively small (e.g., 6.4 μs inAcquisition mode and 1.6 μs in Sleep mode) or conversely the bandwidthof the DDCL 330 is configured relatively large (e.g., 25 KHz inAcquisition mode and 100 KHz in Sleep mode). More generally, STM meansthat DC compensation is performed slower than in FTM, or conversely, FTMmeans that DC compensation is performed faster than in STM.

As discussed in more detail herein, STM is used during the AT connectedstate as it provides an accurate static DC level estimation, but suffersfrom slow acquisition. However, FTM is suitable for acquiring faststatic DC, but suffers from being relatively noisy. FTM is typicallyused during acquisition and sleep modes. However, it may also be used ifthe DC level or power estimation is significantly off. That is, if thereare large fluctuations in the STM, then FTM may be invoked tore-establish a baseline. As mentioned above, the FTM does not provide anaccurate DC level, but is helpful in providing a good initial estimate.It should also be noted that the DC level within the various circuitelements may arise as a function of the updating of the gain stages.That is, each gain stage may introduce a DC component when itsmode/value of operation is changed. Therefore, DC compensation mayinclude consideration of the circuit-introduced DC component. The aboveAGC/DC compensation design enables vast dynamic range accommodation andcan be adjusted according to firmware control.

In modern communication systems, proper DC compensation of the inputsignal is a concern in order to best exploit the dynamic range availablein the ADC. In the UMB standard, as one of several possible standards,the forward link signal strength can significantly vary except forwithin the superframe preamble (SFPA). Since the frame signal strengthis subject to variation and the SFPA is the only stable power levelreference, it poses a great challenge to existing systems trying tocontrol the AGC within the SFPA window. Also, since the residual DClevel of a zero IF receiver varies with the receiver gain settings, DCcompensation should be performed when adjusting the AGC.

In various embodiments disclosed herein, the AGC and the DC compensationare controlled so that receiver gain is distributed in both the analogand digital domains, as well as the DC compensation being applied inboth the analog and digital domains. The DC compensation setting isdependent on the AGC setting; that is, the DC compensation isre-adjusted whenever the analog gain state is changed due to the AGC.

FIG. 4 illustrates a diagram of an exemplary UMB superframe structure410, which may be part of the received signal. The superframe 410 isshown containing a superframe preamble (SFPA). Subsequent to the SFPA,there are 25 forward link PHY frames indexed as 0-24, for example. Anext superframe 420 is illustrated “following” the superframe 410,having a similar preamble and PHY frames.

Each SFPA includes eight (8) symbols with relevant information. Eachsymbol may be approximately 100 microseconds (μs). These symbols includethe Forward-Primary Broadcast Channel (F-PBCCH), four (4)Forward-Secondary Broadcast Channels (F-SBCCH) or four (4) Forward-QuickPage Channels (F-QPCH), and three (3) time-division multiplexed (TDM)Pilots 1-3 (the Forward-Acquisition Channels (F-ACQCH)). For example, asfurther elaborated herein, updating of the AGC is performed during thereception of the F-PBCCH symbol, after this symbol has been decodedand/or with its associated power level. The 3-indexed OFDM symbol is notconsidered critical immediately after acquisition, therefore updating ofthe AGC can be performed immediately after acquisition. Also, the 5-7indexed OFDM symbols are detected and decoded as a SFPA indicator and/orwith power estimation, during acquisition, as the earlier symbols may becorrupted during the initial search. If the 5-7 indexed OFDM symbols aredetected, then it can be confirmed that acquisition has occurred.However, the AGC power levels may be incorrect for this frame,therefore, AGC adjustments may be deferred till the next SFPA.

As apparent from the above discussion, to accommodate the sparseoccurrences of SFPA for received signal strength (RSSI) measurements,the DC compensation and AGC timing parameters are carefully planned tomeet system requirements. In this vein, five modes of operation areimplemented.

DC compensation calibration mode;

Acquisition mode;

Acquisition-to-Connected mode transition;

Connected mode; and

Sleep mode.

DC compensation calibration mode is invoked at power up or any othertimes as desired by the system software (SW)/firmware (FW). DCcompensation calibration is performed for all possible gain states withthe antenna input zeroed out. Here a calibration table can be generatedto offset or compensate for any DC component that is generated throughthe antenna circuitry. This mode can be performed during startup and canbe a FW forced operation. The following describes an exemplary method ofoperating in the DC compensation calibration mode.

FIG. 5 illustrates a flow diagram of an exemplary method 500 ofcalibrating the coarse DC compensation (the ADCL) for all AGC statesaccording to another aspect of the disclosure. According to the method500, the controller 344 detects a power up operation of the accessterminal (AT) (block 502). In response to detecting the power upoperation, the controller 344 opens switch SW1 to disable the antenna302 input to the LNA 304 so that the front-end 300 is not able toreceive a signal (block 504). Then, the controller 344 controls the AGCmodule 332 to configure the LNA 304 in an initial gain state (block506). Then, the controller 344 determines the DC component level at theoutput of the second summer 320 (block 508). Then, the controller 344determines whether all of the gain states have been selected (block510). If all of the LNA gain states have not been selected, the methodproceeds back to block 506 to select the next gain state. Otherwise, thecontroller 344 configures the ADCL 340 so that it performs coarse DCcompensation based on the measured DC components for all the gain states(block 512). Then, the controller 344 closes the switch SW1 so as tocouple the antenna 302 to the LNA 304, so that the front-end 300 is ableto receive a signal (block 514). This method may also apply in additionto, or alternatively, to the gain of the mixer 306.

Acquisition (ACQ) mode is used during initial acquisition or blindsearch. During initial acquisition, no system timing information isavailable to the access terminal (AT). In this case, the acquisitionprocedure is performed parallel to the AGC/DVGA adjustment. In TDDsystems, and due to the absence of timing, the reverse link (RL) framecontributes to energy estimation leading to a large dynamic range ofreceived energy. Add to that channel variations effects; therefore afast tracking/update mode (FTM) that tries to follow closely energyvariations in the signal is implemented. Another way of explaining thisis that DC compensation is set to FTM mode. In each update cycle, DCcompensation performs FTM update and the AGC conducts energy estimation(EE) or RSSI measurement until tracking is obtained. Once the accessterminal (AT) acquires the timing, the superframe (SF) boundaries arewell defined at this point, and the AGC/DVGA moves to the slow trackingmode (STM), subject to other conditions explained below.

Acquisition-to-Connected-Transition Mode: Once the access terminal (AT)has acquired the system time, the access terminal (AT) stops AGCoperation until the next SFPA. At the start of the SFPA, the DCcompensation and AGC run a series of (configurable) ACQ cycles, e.g., DCcompensation FTM followed by EE/AGC update. Afterwards, it switches toConnected mode with DC compensation changed to STM mode with DCcompensation coarse loop enabled. The following describes an exemplarymethod of operating in the acquisition andacquisition-to-connected-transition mode.

FIG. 6 illustrates a flow diagram of an exemplary method 600 ofperforming AGC and DC level compensation in acquisition andacquisition-to-connected-transition modes according to another aspect ofthe disclosure. According to the method 600, the controller 344 detectsthat an RF signal is being received (block 602). In response todetecting the received signal, the controller 344 instructs the DDCL 330to perform a fine adjustment in FTM (e.g., ˜26 microseconds (μs) lengthoperation) to reduce the DC component at the output of the second summer320 (block 604). Then, the controller 344 instructs the AGC module 332to perform a relatively short energy estimation (e.g., ˜26 μs lengthoperation) (block 606), and generates an AGC signal to adjust the gainof the LNA 304 (and/or the mixer 306) based on the energy estimation(e.g., ˜6 μs length operation) (block 608). Then, the controller 344determines whether the digital signal processing module 342 has acquiredthe timing of the received signal (block 610). If it has not, then theoperations in blocks 604-610 are repeated.

If, on the other hand, the digital signal processing module 342 hasacquired the timing of the received signal, it sends a signal to thecontroller 344 that it is processing the superframe preamble (SFPA)(block 614). Then, the controller 344 sets an iteration or count to one(1) (block 616). The controller 344 instructs the DDCL 330 to perform afine adjustment in FTM (e.g., ˜26 μs length operation) to reduce the DCcomponent at the output of the second summer 320 (block 618). Then, thecontroller 344 instructs the AGC module 332 to perform a relativelyshort energy estimation (e.g., ˜26 μs length operation) (block 620), andto generate an AGC signal to adjust the gain of the LNA 304 (and/or themixer 306) based on the energy estimation (e.g., ˜6 μs length operation)(block 622). The controller 344 then determines whether the iteration orcount is equal to a predetermined limit (e.g., five (5) or six (6))(block 624). If the iteration or count is not equal to the predeterminedlimit, the controller 344 increments the iteration or count (block 626).The controller 344 then repeats the operations of blocks 618 to 624. If,on the other hand, the controller 344 determines that the iteration orcount is equal to the predetermined limit, the controller 344 ends theacquisition AGC/DC adjust processes (block 628).

Connected Mode entails two sub-modes: SFPA before PBCCH decode and SFPAafter PBCCH decode.

First, a discussion of the general concept behind the “before” PBCCHdecode mode is commenced, which starts with AGC energy estimation of theRSSI signal with DC compensation in slow tracking/update mode (STM) atthe beginning of the 4th OFDM symbol of the SFPA. Afterwards, if theresidual DC value crosses a pre-determined threshold, the operationswitches from STM to FTM mode and begins to perform a pre-determinednumber of DC compensation coarse loop updates before switching the DCcompensation back to STM.

Connected Mode for SFPA after PBCCH decode: We start AGC Energy Estimate(RSSI) with DC compensation in STM at the beginning of the first OFDMsymbol of the SFPA. Afterwards, if the residual DC value crosses apre-determined threshold, then we switch from STM to FTM mode and do apre-determined number of DC compensation coarse loop updates beforeswitching DC compensation back to STM.

In connected mode, there is the possibility of transmitting less thanfull power between preambles. Therefore, any update between twosuperframes can cause the ADC to saturate. For example, this may occurif an update is performed at a partial power frame followed by a fullpower frame. So, to avoid this pitfall, it is desired to update thesuperframe only during the preambles. It should be noted that the AGCmay be running during the whole superframe(s), but is only updatedduring the preambles. Also, instead of locking to an instantaneousvalue, the AGC is locked to a filtered value. After ACQ, theinstantaneous energy is calculated from other than the 1^(st)-3^(rd)symbols (0-2^(nd) indexed) in the amplifier until PBCCH decoding, thenfrom the first OFDM symbol afterwards. Here, it is presumed that timinghas been accomplished. The following describes an exemplary method ofoperating in the connected mode.

FIG. 7 illustrates a flow diagram of an exemplary method 700 ofperforming AGC and DC level compensation in connected mode according toanother aspect of the disclosure. According to the method 700, thecontroller 344 receives a message from the digital signal processingmodule 342 indicating the detection of the first (1^(st)) OFDM symbol ofthe SFPA (if the PBCCH symbol has already been decoded) or the fourth(4^(th)) OFDM of the SFPA (if the PBCCH symbol has not yet been decoded)(block 702). If the corresponding symbol has not been detected, thencontroller 344 keeps on monitoring for the detection of this symbol perblock 702. If the first (1^(st)) or fourth (4^(th)) symbol has beendetected, the controller 344 instructs the AGC module 332 to perform arelatively long energy estimation of the received RF signal at the inputto the LNA 304 (e.g., ˜52 μs length operation) (block 704). Based on theenergy estimation, the AGC module 332 determines whether the gain of theLNA 304 (and/or the mixer 306) needs to be adjusted (block 706). If itdoes, then the AGC module 332 generates an AGC signal to adjust the gainof the LNA 304 (and/or the mixer 306) based on the energy estimation(e.g., ˜6 μs length operation). The method 700 then proceeds tooperation depicted in block 710.

If the AGC module 332 determines that the gain of the LNA 304 (and/orthe mixer 306) need not be adjusted in block 706, then the controller344 determines the DC component at the output of the second summer 320(block 714). Then, the controller 344 determines whether the DCcomponent exceeds a predetermined threshold (block 716). If it does not,the controller 344 returns to the operation of block 702 to detect thefirst (1^(st)) or fourth (4^(th)) symbol of the next SFPA. If, on theother hand, the controller 344 determines that the measured DC componentexceeds the predetermined threshold in block 716, the controller 344instructs the DDCL 330 to perform a fine adjustment in STM to reduce theDC component at the output of the second summer 320 (e.g., ˜6.5 μslength operation) (block 710). Then, the controller 344 instructs theADCL 340 to perform one or two coarse adjustments to reduce the DCcomponent at the output of the second summer 320 (e.g., ˜6.5 μs lengthoperation) (block 712). The controller 344 then returns to the operationof block 702 to detect the first (1^(st)) or fourth (4^(th)) symbol ofthe next SFPA.

Finally, Sleep Mode (Wakeup from Sleep): In this mode, the system wakesup at the beginning of the SFPA. Then, a DC update is performed in FTMand then perform EE. This procedure of DC/EE is repeated for apre-determined number of cycles, upon which the process switches DCcompensation to the STM mode. The following describes an exemplarymethod of operating in the sleep mode.

FIG. 8 illustrates a flow diagram of an exemplary method 800 ofperforming AGC and DC level compensation in sleep mode according toanother aspect of the disclosure. According to the method 800, thedigital signal processing module 342 wakes up to check whether there isa page for the access terminal (AT) (block 802). After it has woke up,the digital signal processing module 342 detects the first (1^(st)) OFDMsymbol of the SFPA (block 804). After being notified of the detection ofthe first (1^(st)) OFDM symbol, the controller 344 sets the iteration orcount to one (1) (block 806). Then, the controller 344 instructs theDDCL 330 to perform a fine adjustment in FTM to reduce the DC componentat the output of the second summer 320 (e.g., ˜6.5 μs length operation)(block 808). Next, the controller 344 instructs the AGC module 332 toperform a relatively very short energy estimation (e.g., ˜6.5 μs lengthoperation) (block 810). The AGC module 332 then generates an AGC signalto adjust the gain of the LNA 304 (and/or the mixer 306) based on theenergy estimation (e.g., ˜6.5 μs length operation) (block 812). Thecontroller 344 then determines whether the iteration or count equals apredetermined limit (e.g., five (5) or six (6)) (block 814). If itdetermines that the iteration or count does not equal the predeterminedlimit, the controller 344 increments the iteration or count (block 818),and repeats the operations in blocks 808 to 814. Otherwise, thecontroller 344 ends the sleep AGC/DC adjustment process (block 816).

Some of the rationales for the sequence of operations of the above modesare detailed herein. When acquisition cycle/timing is confirmed, fasttracking (FTM) is stopped until the next (second) superframe, at whichfast tracking (FTM) is restarted for a pre-determined number of cyclesin order to get a good initial estimate of the power setting in thepreamble. It is understood that the first segments of the initialacquisition information may be corrupted or the power level for thefirst superframe preamble may be different than the next arriving(second) superframe preamble. Therefore, fast tracking is restarted atthe next (second) superframe preamble (after timing has been acquired)in order to get a good initial power estimate. It is noted that AGCupdates should not be performed between superframe preambles, butperformed during the preambles, as the energy levels in the preamblesare presumed to be constant.

However, because the 1^(st) symbol in the next (second) superframepreamble may also be corrupted or have a different power from that ofthe first superframe preamble, it is typically discarded. Because timinghas been acquired, the fast tracking mode will quickly assess the powerin the subsequent symbols in the next (second) superframe preamble.Thereafter, slow tracking mode (STM) can be performed.

With timing already acquired and power determined in the next (second)superframe preamble, the 1^(st) symbol of the preamble becomesirrelevant and updating of the AGC can now be performed on the 1^(st)symbol of the next (third) arriving superframe preamble.

FIG. 9 illustrates a block diagram of exemplary AGC module 900 accordingto another aspect of the disclosure. The AGC module 900 may be oneexemplary implementation of the AGC module 332 (but further includes thedigital gain module as item 922). The digital gain module 922 may be thesame module 328 of front-end system 300, previously discussed.

In particular, the controller 900 comprises an energy estimator (EE)902, a linear-to-log 2 transformer 904, a summer 906, a first (1^(st))order filter 907, a divider/subtractor 918, and logic 920. The EE 902receives the input signal from DC compensation/correction and forwardsthe signal to the transformer 904 to convert it to a log based format.The output of the transformer 904 is fed into the summer 906 havinganalog gain (log 2 format) as a reversed input. The analog gain (Log 2)estimates the gain between the antenna port to the input of the summer906. Thus, the output of the summer 906 will be an updated energyestimate E(n) of the received RF signal at the antenna port.

The output of the summer 906 is applied to the first (1^(st)) orderfilter 907, which removes noise from the energy estimate E(n) of thereceived signal, and generate an average energy estimate Ē(n) of thereceived signal. The first (1^(st)) order filter 907 may, in turn,comprise a first multiplier 908, a summer 910, a delay element Z⁻¹ 916,and a second multiplier 914. The energy estimate E(n) of the receivedsignal is applied to the first multiplier 908, which scales the estimateE(n) by a factor of 1−α. The scaled estimate is then applied to thesummer 910, which sums it with a feedback signal from the output of thesecond multiplier 914. The average energy estimate Ē(n) of the receivedsignal is generated at the output of the summer 910, which is applied tothe input of the delay element Z⁻¹ 916. The output of the delay elementt Z⁻¹ 916 is coupled to the second multiplier 914, which scales thedelayed average energy estimate Ē(n) by a factor of α to generate thefeedback signal.

The output of the filter 907 is fed into the divider/subtractor 918(subtraction in log domain is equivalent to division in linear domain).A reference level or target level E_(ref) is input into thedivider/subtractor 918. The output of the divider/subtractor 918provides a gain ratio result and is then fed into logic 920. Logic 920has two outputs, one being digital gain signal d(n) for input into ofthe digital gain module 922 and one being analog gain signal f(n) forAGC control.

In summary, the DVGA operates on the energy signal after rejectinginterference. The energy estimation is first scaled down by the currentanalog gain to obtain the received signal power level (before applyingany gain). A first order loop is then used to estimate a filtered valueof the power level. The control logic will select the correspondinganalog gain stage by locating the RSSI. By using the arrangement shownin FIG. 9, it is possible to jump multiple analog gain stages in oneupdate which provides faster AGC settling. It should be appreciated thatvarious elements shown in FIG. 9 may be altered or changed according todesign preference, while enabling the desired effective level ofperformance. Therefore, modifications may be made without departing fromthe spirit and scope of this and other embodiments.

FIG. 10 illustrates a block diagram of exemplary direct current (DC)compensation loops 1000 according to another aspect of the disclosure.Two loops are shown in 1000 representing feedback loops 1010 and 1050with bandwidth control constants K_(i) and K_(o) as respective inputs.The first loop 1010 is considered a fine DC adjustment loop, while thesecond loop 1050 is considered a coarse DC adjustment loop.

In particular, the fine DC adjustment loop 1010 comprises a summer 1012adapted to sum the signal x_(l)(n) from the output of the second summer320 with a feedback signal d_(l)(n) to generate a DC compensation signaly_(l)(n). The DC compensation signal y_(l)(n) is applied to themultiplier 1014, which scales the signal by the bandwidth controlconstant K_(i). The scaled signal is then applied to a summer 1016,which sums the scaled signal with a delayed output of the summer 1016provided by delay element Z⁻¹ 1018. The feedback signal d_(l)(n) isgenerated at the output of the delay element Z⁻¹ 1018.

The coarse DC adjustment loop 1050 comprises a multiplier 1052 adaptedto multiply the feedback signal d_(l)(n) from the fine DC adjustmentloop 1010 with the bandwidth control constant K_(o). The scaled signalis then applied to a summer 1054, which sums the scaled signal with theDC coarse compensation signal a_(l)(n). The DC coarse adjustment signala_(I)(n) is generated by delaying the output of the summer 1054 usingdelay element Z⁻¹ 1056. The Q-DC coarse adjustment signal a_(I)(n) isgenerated in a similar fashion. Both the I- and Q-DC coarse adjustmentsignal a_(I)(n) and a_(Q)(n) are applied to inputs of a DAC 1060, whichgenerates the analog DC coarse adjustment signal a_(a)(n).

It should be appreciated that the loop algorithms represented by theinternal workings of the loops may be changed according to designpreference. Therefore, while FIG. 10 illustrates one particularembodiment for DC loop design, other implementation may be used, whereinmultiple loops or multiple degrees of granularity in control can beaccomplished.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an example of exemplary approaches. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, changes in energy states, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentdisclosure. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the disclosure. Thus, the present disclosure is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. An apparatus for processing a received radio frequency (RF) signal,comprising: an RF device for processing the received RF signal togenerate a downconverted signal; an energy estimator coupled to the RFdevice for providing a signal related to an energy estimate of thereceived RF signal; an automatic gain control (AGC) module comprisingthe energy estimator and a digital variable gain amplifier (DVGA), theDVGA of the AGC module for controlling the gain of the RF device basedon the energy estimate signal; a fine DC compensation module coupled tothe RF device for performing fine adjustment of a DC component in thedownconverted received signal, wherein a signal output from the DVGA ofthe AGC module controls the fine DC compensation module to perform thefine adjustment; a coarse DC compensation module coupled to the RFdevice for performing coarse adjustment of the DC component in thedownconverted received signal, wherein a signal output from the DVGA ofthe AGC module controls the coarse DC compensation module to perform thecoarse adjustment; an analog-to-digital converter (ADC) coupled to theRF device for converting the downconverted received signal from ananalog domain to a digital domain; and a digital gain module coupled tothe ADC and adapted to adjust the level of the downconverted receivedsignal in the digital domain, wherein the AGC module is adapted tocontrol the digital gain module based on the energy estimate signal. 2.The apparatus of claim 1, wherein the RF device comprises a low noiseamplifier (LNA).
 3. The apparatus of claim 1, wherein the RF devicecomprises a mixer.
 4. The apparatus of claim 1, wherein the AGC modulecontrols the gain of the RF device in a predetermined set of gains. 5.The apparatus of claim 1, wherein the fine DC compensation moduleperforms fine adjustment of the DC component in the downconvertedreceived signal in a fast tracking mode (FTM) or slow tracking mode(STM).
 6. The apparatus of claim 1, wherein the fine DC compensationmodule performs fine adjustment of the DC component in the downconvertedreceived signal in the digital domain.
 7. The apparatus of claim 1,wherein the coarse DC compensation module performs coarse adjustment ofthe DC component in the downconverted received signal in the analogdomain.
 8. The apparatus of claim 3, further comprising a controllercoupled to the coarse DC compensation module and adapted to configurethe coarse DC compensation module based on a series of measurements ofDC level from the AGC module corresponding to a series of gain states,when the RF received signal is not present.
 9. An apparatus forprocessing a received radio frequency (RF) signal, comprising: an RFdevice for processing the received RF signal to generate a downconvertedsignal; an energy estimator coupled to the RF device for providing asignal related to an energy estimate of the received RF signal; anautomatic gain control (AGC) module comprising the energy estimator anda digital variable gain amplifier (DVGA), the DVGA of the AGC module forcontrolling the gain of the RF device based on the energy estimatesignal; a fine DC compensation module coupled to the RF device forperforming fine adjustment of a DC component in the downconvertedreceived signal, wherein a signal output from the DVGA of the AGC modulecontrols the fine DC compensation module to perform the fine adjustment;a coarse DC compensation module coupled to the RF device for performingcoarse adjustment of the DC component in the downconverted receivedsignal, wherein a signal output from the DVGA of the AGC module controlsthe coarse DC compensation module to perform the coarse adjustment; asignal processing module coupled to the RF device for detecting timinginformation in the downconverted received signal; and a controllercoupled to the signal processing module, wherein in response to thesignal processing module not detecting the timing information in thedownconverted received signal, the controller is adapted to perform oneor more iterations of the following sequential operations: instruct thefine DC compensation module to perform a fine adjustment in a fasttracking mode (FTM) of the DC component in the downconverted receivedsignal; instruct the energy estimator to generate an energy estimate ofthe received RF signal; and instruct the AGC module to control the gainof the RF device based on the energy estimate signal.
 10. The apparatusof claim 9, wherein in response to the signal processing moduledetecting the timing information in the downconverted received signal,the controller is adapted to perform a predetermined number of one ormore iterations of the following sequential operations: instruct thefine DC compensation module to perform a fine adjustment in the FTM ofthe DC component in the downconverted received signal; instruct theenergy estimator to generate an energy estimate of the received RFsignal; and instruct the AGC module to control the gain of the RF devicebased on the energy estimate signal.
 11. An apparatus for processing areceived radio frequency (RF) signal, comprising: an RF device forprocessing the received RF signal to generate a downconverted signal; anenergy estimator coupled to the RF device for providing a signal relatedto an energy estimate of the received RF signal; an automatic gaincontrol (AGC) module comprising the energy estimator and a digitalvariable gain amplifier (DVGA), the DVGA of the AGC module forcontrolling the gain of the RF device based on the energy estimatesignal; a fine DC compensation module coupled to the RF device forperforming fine adjustment of a DC component in the downconvertedreceived signal, wherein a signal output from the DVGA of the AGC modulecontrols the fine DC compensation module to perform the fine adjustment;a coarse DC compensation module coupled to the RF device for performingcoarse adjustment of the DC component in the downconverted receivedsignal, wherein a signal output from the DVGA of the AGC module controlsthe coarse DC compensation module to perform the coarse adjustment; asignal processing module coupled to the RF device for detecting timinginformation in the downconverted received signal; and a controllercoupled to the signal processing module and adapted to perform thefollowing sequential operations: instruct the energy estimator togenerate an energy estimate of the received RF signal in a timingrelationship with the downconverted received signal; and instruct theAGC module to control the gain of the RF device based on the energyestimate signal in the timing relationship with the downconvertedreceived signal.
 12. The apparatus of claim 11, wherein the controlleris further adapted to perform the following operations: instruct thefine DC compensation module to perform a fine adjustment in a slowtracking mode (STM) of the DC component in the downconverted receivedsignal in the timing relationship with the downconverted receivedsignal; and instruct the coarse DC compensation module to perform acoarse adjustment of the DC component in the downconverted receivedsignal in the timing relationship with the downconverted receivedsignal.
 13. The apparatus of claim 12, wherein the timing relationshipcomprises a time interval for the signal processing module to process atleast a portion of a superframe preamble of the downconverted receivedsignal.
 14. An apparatus for processing a received radio frequency (RF)signal, comprising: an RF device for processing the received RF signalto generate a downconverted signal; an energy estimator coupled to theRF device for providing a signal related to an energy estimate of thereceived RF signal; an automatic gain control (AGC) module comprisingthe energy estimator and a digital variable gain amplifier (DVGA), theDVGA of the AGC module for controlling the gain of the RF device basedon the energy estimate signal; a fine DC compensation module coupled tothe RF device for performing fine adjustment of a DC component in thedownconverted received signal, wherein a signal output from the DVGA ofthe AGC module controls the fine DC compensation module to perform thefine adjustment; a coarse DC compensation module coupled to the RFdevice for performing coarse adjustment of the DC component in thedownconverted received signal, wherein a signal output from the DVGA ofthe AGC module controls the coarse DC compensation module to perform thecoarse adjustment; a signal processing module coupled to the RF devicefor detecting timing information in the downconverted received signal;and a controller coupled to the signal processing module and adapted toperform the following operations if the DC component of thedownconverted received signal exceeds a predetermined threshold:instruct the fine DC compensation module to perform a fine adjustment ina slow tracking mode (STM) of the DC component in the downconvertedreceived signal in a timing relationship with the downconverted receivedsignal; and instruct the coarse DC compensation module to perform acoarse adjustment of the DC component in the downconverted receivedsignal in the timing relationship with the downconverted receivedsignal.
 15. An apparatus for processing a received radio frequency (RF)signal, comprising: an RF device for processing the received RF signalto generate a downconverted signal; an energy estimator coupled to theRF device for providing a signal related to an energy estimate of thereceived RF signal; an automatic gain control (AGC) module comprisingthe energy estimator and a digital variable gain amplifier (DVGA), theDVGA of the AGC module for controlling the gain of the RF device basedon the energy estimate signal; a fine DC compensation module coupled tothe RF device for performing fine adjustment of a DC component in thedownconverted received signal, wherein a signal output from the DVGA ofthe AGC module controls the fine DC compensation module to perform thefine adjustment; a coarse DC compensation module coupled to the RFdevice for performing coarse adjustment of the DC component in thedownconverted received signal, wherein a signal output from the DVGA ofthe AGC module controls the coarse DC compensation module to perform thecoarse adjustment; a signal processing module coupled to the RF devicefor detecting timing information in the downconverted received signal;and a controller coupled to the signal processing module and adapted toperform a predetermined one or more iterations of the followingsequential operations: instruct the fine DC compensation module toperform a fine adjustment in a fast tracking mode (FTM) of the DCcomponent in the downconverted received signal in a timing relationshipwith the downconverted received signal; instruct the energy estimator togenerate an energy estimate of the received RF signal in the timingrelationship with the downconverted received signal; and instruct theAGC module to control the gain of the RF device based on the energyestimate signal in the timing relationship with the downconvertedreceived signal.
 16. The apparatus of claim 15, wherein the timingrelationship comprises a time interval for the signal processing moduleto process at least a portion of a superframe preamble of thedownconverted received signal.
 17. A method of processing a receivedradio frequency (RF) signal for adjusting a programmable power gain,comprising: generating a signal related to an energy estimate of thereceived RF signal; controlling the programmable power gain byamplifying a digital variable gain based on the energy estimate signal;downconverting the received RF signal; adjusting a DC component of thedownconverted signal in a relatively fine manner, wherein the amplifieddigital variable gain controls the adjustment in the relatively finemanner; adjusting the DC component of the downconverted signal in arelatively coarse manner, wherein the amplified digital variable gaincontrols the adjustment in the relatively coarse manner; performing oneor more iterations of the following sequential operations prior todetecting timing information in the downconverted signal: adjusting theDC component of the downconverted signal in the relatively fine mannerand in a fast tracking mode (FTM), generating the signal related to theenergy estimate of the received RF signal, and controlling theprogrammable power gain based on the energy estimate signal; anddetecting the timing information in the downconverted signal.
 18. Themethod of claim 17, further comprising performing a predetermined numberof one or more iterations of the following sequential operations afterdetecting the timing information in the downconverted signal: adjustingthe DC component of the downconverted signal in the relatively finemanner and in the FTM; generating the signal related to the energyestimate of the received RF signal; and controlling the programmablepower gain based on the energy estimate signal.
 19. A method ofprocessing a received radio frequency (RF) signal for adjusting aprogrammable power gain, comprising: generating a signal related to anenergy estimate of the received RF signal; controlling the programmablepower gain by amplifying a digital variable gain based on the energyestimate signal; downconverting the received RF signal; adjusting a DCcomponent of the downconverted signal in a relatively fine manner,wherein the amplified digital variable gain controls the adjustment inthe relatively fine manner; adjusting the DC component of thedownconverted signal in a relatively coarse manner, wherein theamplified digital variable gain controls the adjustment in therelatively coarse manner; detecting timing information in thedownconverted signal; generating the signal related to the energyestimate of the received RF signal in a timing relationship with thedownconverted signal; and controlling the programmable power gain basedon the energy estimate signal in the timing relationship with thedownconverted signal.
 20. The method of claim 19, further comprising:adjusting the DC component of the downconverted signal in the relativelyfine manner and in a slow tracking mode (STM) in a timing relationshipwith the downconverted signal; and adjusting the DC component of thedownconverted signal in the relatively coarse manner in the timingrelationship with the downconverted signal.
 21. The method of claim 20,wherein the timing relationship comprises a time interval for processingat least a portion of a superframe preamble of the downconverted signal.22. A method of processing a received radio frequency (RF) signal foradjusting a programmable power gain, comprising: generating a signalrelated to an energy estimate of the received RF signal; controlling theprogrammable power gain by amplifying a digital variable gain based onthe energy estimate signal; downconverting the received RF signal;adjusting a DC component of the downconverted signal in a relativelyfine manner, wherein the amplified digital variable gain controls theadjustment in the relatively fine manner; adjusting the DC component ofthe downconverted signal in a relatively coarse manner, wherein theamplified digital variable gain controls the adjustment in therelatively coarse manner; detecting timing information in thedownconverted signal; and performing a predetermined number of one ormore iterations of the following sequential operations: adjusting the DCcomponent of the downconverted signal in the relatively fine manner andin a fast tracking mode (FTM) in a timing relationship with thedownconverted signal; generating the signal related to the energyestimate of the received RF signal in the timing relationship with thedownconverted signal; and controlling the programmable power gain basedon the energy estimate signal in the timing relationship with thedownconverted signal.
 23. The method of claim 22, wherein the timingrelationship comprises a time interval for processing at least a portionof a superframe preamble of the downconverted signal.
 24. An apparatusfor processing a received radio frequency (RF) signal for adjusting aprogrammable power gain, comprising: means for generating a signalrelated to an energy estimate of the received RF signal; means forcontrolling the programmable power gain by amplifying a digital variablegain based on the energy estimate signal; means for downconverting thereceived RF signal; means for adjusting a DC component of thedownconverted signal in a relatively fine manner, wherein the amplifieddigital variable gain controls the adjustment in the relatively finemanner; means for adjusting the DC component of the downconverted signalin a relatively coarse manner, wherein the amplified digital variablegain controls the adjustment in the relatively coarse manner; means forcontrolling the following in a sequential order prior to detectingtiming information in the downconverted signal: means for adjusting theDC component of the downconverted signal in the relatively fine mannerand in a fast tracking mode (FTM), means for generating the signalrelated to the energy estimate of the received RF signal, and means forcontrolling the programmable power gain based on the energy estimatesignal; and means for detecting the timing information in thedownconverted signal.
 25. An apparatus for processing a received radiofrequency (RF) signal for adjusting a programmable power gain,comprising: means for generating a signal related to an energy estimateof the received RF signal; means for controlling the programmable powergain by amplifying a digital variable gain based on the energy estimatesignal; means for downconverting the received RF signal; means foradjusting a DC component of the downconverted signal in a relativelyfine manner, wherein the amplified digital variable gain controls theadjustment in the relatively fine manner; means for adjusting the DCcomponent of the downconverted signal in a relatively coarse manner,wherein the amplified digital variable gain controls the adjustment inthe relatively coarse manner; means for detecting timing information inthe downconverted signal; and means for controlling the following in atiming relationship with the downconverted signal after the timinginformation in the downconverted signal is detected: means forgenerating the signal related to the energy estimate of the received RFsignal in the timing relationship with the downconverted signal; andmeans for controlling the programmable power gain based on the energyestimate signal in the timing relationship with the downconvertedsignal.
 26. The apparatus of claim 25, wherein the controlling meansadditionally controls the following in the timing relationship with thedownconverted signal after the timing information in the downconvertedsignal is detected: means for adjusting the DC component of thedownconverted signal in the relatively fine manner and in a slowtracking mode (STM); and means for adjusting the DC component of thedownconverted signal in the relatively coarse manner.
 27. An apparatusfor processing a received radio frequency (RF) signal for adjusting aprogrammable power gain, comprising: means for generating a signalrelated to an energy estimate of the received RF signal; means forcontrolling the programmable power gain by amplifying a digital variablegain based on the energy estimate signal; means for downconverting thereceived RF signal; means for adjusting a DC component of thedownconverted signal in a relatively fine manner, wherein the amplifieddigital variable gain controls the adjustment in the relatively finemanner; means for adjusting the DC component of the downconverted signalin a relatively coarse manner, wherein the amplified digital variablegain controls the adjustment in the relatively coarse manner; means fordetecting timing information in the downconverted signal; and means forcontrolling a predetermined one or more iterations of the following in atiming relationship with the downconverted signal: means for adjustingthe DC component of the downconverted signal in the relatively finemanner and in a fast tracking mode (FTM); means for generating thesignal related to the energy estimate of the received RF signal; andmeans for controlling the programmable power gain based on the energyestimate signal.
 28. A computer readable program product for processinga received radio frequency (RF) signal for adjusting a programmablepower comprising a computer-readable medium having instructions storedthereon, the instructions being executable by one or more processors andcomprising: instructions for generating a signal related to an energyestimate of the received RF signal; instructions for controlling theprogrammable power gain by amplifying a digital variable gain based onthe energy estimate signal; instructions for downconverting the receivedRF signal; instructions for adjusting a DC component of thedownconverted signal in a relatively fine manner, wherein the amplifieddigital variable gain controls the adjustment in the relatively finemanner; instructions for adjusting the DC component of the downconvertedsignal in a relatively coarse manner, wherein the amplified digitalvariable gain controls the adjustment in the relatively coarse manner;instructions for detecting timing information in the downconvertedsignal; instructions for generating the signal related to the energyestimate of the received RF signal in a timing relationship with thedownconverted signal; and instructions for controlling the programmablepower gain based on the energy estimate signal in the timingrelationship with the downconverted signal.